Liquid phase epoxidation process

ABSTRACT

The present invention provides a continuous process for the epoxidation of an olefinic compound with an oxidant, which process comprises reaction of an olefinic compound with an oxidant in the presence of a catalyst in an apparatus that comprises
         a reactive distillation column, which column comprises
           (i) a reactive section, which comprises the catalyst   (ii) a rectifying section situated above the reactive section and adapted to allow separation of reagents and/or by-products from products   (vii) a stripping section situated below the reactive section and adapted to allow   
           separation of product from reagents and/or by-products
           (viii) a vessel situated below the stripping section and adapted to provide a source of heat for the column and in which initial vaporisation of one or more of the reagents can occur,   
           wherein the temperature in the reactive section (i) is a temperature at which the reaction between the olefinic compound and the oxidant takes place and the temperature in the stripping section (iii) is higher than the temperature in the rectifying section (ii).

This application is a divisional of U.S. patent application Ser. No.13/388,065 filed on Jan. 31, 2012, which is a 371 of PCT/GB2010/001458filed on Jul. 30, 2010 and claims priority to United Kingdom No.0913318.2 filed on Jul. 31, 2009, which are hereby incorporated hereinby reference in their entirety.

The present invention relates a process for the continuous epoxidationof olefinic compounds and to apparatus for use in that process.

Epoxides are versatile and useful intermediates in organic synthesis.The epoxidation of olefinic compounds is a well known process which isoperated industrially. For example, the use of a soluble molybdenumcatalyst or a heterogeneous titanium/silica catalyst for the epoxidationof propylene to propylene oxide using alkyl hydroperoxide is known.

An industrial example of the use of Mo(IV) complexes is the HalconProcess, which uses a soluble Mo complex to catalyse the formation ofpropylene oxide from propylene highly selectively in the liquid phase at373 K. This process is described in U.S. Pat. No. 3,351,635.

Currently, many epoxidation reactions can only be performed using batchreactions, which can limit the scope of the reaction. Problemsassociated with large scale batch reactions when compared to smallerlaboratory based reactions include reduced efficiency, use of largequantities of solvents, temperature control issues, high unit cost anduse of large quantities of potentially explosive oxidants such asperacid oxidants, which is both potentially dangerous and alsopotentially harmful to the environment.

U.S. Pat. No. 5,420,313 describes the use of polymer supportedmolybdenum, tungsten, vanadium and titanium complexes in the conversionof olefinic compounds to their epoxide in the presence of a peroxide.

The listing or discussion of an apparently prior-published document inthis specification should not necessarily be taken as an acknowledgementthat the document is part of the state of the art or is common generalknowledge

However, despite the success with immobilised catalysts in small scaleepoxidation reactions, there have been no significant attempts toprovide medium to large scale production using this technology. Reasonsfor this include the concern that in continuous processes apparentlylong-lived heterogeneous catalysts may prove to be unstable, with evenlow levels of metal leaching causing problems.

Therefore there is a need for an epoxidation process which does notresult in the polymer supported catalyst becoming unstable.

Further, there remains a need to provide alternative epoxidationprocesses which can be performed on a large scale and which avoid one ormore of the problems associated with large scale batch reactions.

It is an object of the invention to solve one or more of these problems.

The present invention provides a continuous process for the epoxidationof olefins, for example alkenes and terpenes. In this process theolefinic compound is reacted with an oxidant in the presence of apolymer supported catalyst in a reactive distillation column.

More particularly, the present invention provides a continuous processfor the epoxidation of an olefinic compound with an oxidant, whichprocess comprises reaction of an olefinic compound with an oxidant inthe presence of a catalyst in an apparatus that comprises

-   -   a reactive distillation column, which column comprises    -   (i) a reactive section, which comprises the catalyst    -   (ii) a rectifying section situated above the reactive section        and adapted to allow separation of reagents and/or by-products        from products    -   (iii) a stripping section situated below the reactive section        and adapted to allow    -   separation of product from reagents and/or by-products    -   (iv) a vessel situated below the stripping section and adapted        to provide a source of heat for the column and in which initial        vaporisation of one or more of the reagents can occur,    -   wherein the temperature in the reactive section (i) is a        temperature at which the reaction between the olefinic compound        and the oxidant takes place and the temperature in the stripping        section (iii) is higher than the temperature in the rectifying        section (ii).

The present invention also provides an apparatus in which the continuousliquid phase epoxidation of an olefinic compound with an oxidant cantake place. This apparatus comprises

-   -   a reactive distillation column, which column comprises    -   (i) a reactive section, which is adapted so that it can contain        the catalyst    -   (ii) a rectifying section situated above the reactive section        and adapted to allow separation of reagents and/or by-products        from products    -   (v) a stripping section situated below the reactive section and        adapted to allow    -   separation of product from reagents and/or by-products    -   (vi) a vessel situated below the stripping section and adapted        to provide a source of heat for the column and in which initial        vaporisation of one or more of the reagents can occur.

As used herein, when we refer to “products” we mean the desirableproducts of the reaction. Undesirable products are referred to as“by-products”.

The inventors have surprisingly found that the use of apolymer-supported molybdenum catalyst in a reactive distillation columncan provide efficient and selective epoxidation of olefinic compoundssuch as alkenes and terpenes.

Catalyst compositions suitable for use in the process of presentinvention include those comprising one or more metals complexed to anorganic or inorganic support through the intermediacy of a ligand suchas a nitrogen based ligand molecule, for example an imidazole ligand.Suitable catalysts include those comprising at least one of titanium,vanadium, molybdenum, tungsten, manganese, iron, ruthenium and copper.Preferably the catalyst composition comprises at least one ofmolybdenum, titanium, vanadium and/or tungsten. Most preferably thecatalyst comprises molybdenum. More than one metal may be present in thecatalyst composition.

Suitable catalysts include those described in U.S. Pat. No. 5,420,313.

The catalyst is typically complexed to an organic or inorganic supportthrough the intermediacy of an imidazole ligand. The imidazole ligandmay comprise unsubstituted imidazole or a substituted imidazole such as2-pyridyl-2-imidazole, benzimidazole, 5-5′-bibenzimidazole, carboxylicacid and hydroxyl substituted imidazoles and benzimidazoles. Theimidazole ligand may be attached to the support through any part of theimidazole or substituted imidazole provided that the imidazole ring isavailable for complexing to the metal of the catalyst. The imidazoleligand may comprise part of the support rather than being pendantthereto; for example the imidazole may comprise part of a polymerrepeating unit.

A preferred class of polymers for use in the catalysts used in thepresent invention are polybenzimidazoles, such aspoly[2,2′(m-phenylene)-5,5′-bibenzimidazole], which is a polymer havinga repeating unit represented by the formula (I). In a preferred aspectof the invention the catalyst is a polybenzimidazole supported catalyst.It is preferred that the polybenzimidazole ispoly[2,2′(m-phenylene)-5,5′-bibenzimidazole].

If an organic support is used it may be any suitable polymer such as onewhich is stable under the reaction conditions used in the process of theinvention. Suitable polymer supports include but are not limited tostyrene polymers, methacrylate polymers, glycidyl methacrylate polymers,benzimidazole polymers, polyimides, polybenzothiazoles, polybenzoxazolesand optionally copolymers with suitable co-monomers, optionally thepolymers may be cross-linked.

The support may comprise a functionalised inorganic support such asfunctionalised silica or alumina.

Preferably the support comprises benzimidazole.

An example of a suitable catalyst support is polystyrene2-(aminomethyl)pyridine.

As described in U.S. Pat. No. 5,420,313, the catalyst composition may beprepared by effecting a ligand exchange reaction between anorganometallic complex of a metal as listed above having a suitableleaving group with a support having a nitrogen based ligand, such asimidazole.

The catalyst used in the process of the present invention may beactivated before use by oxidising with a suitable oxidant, such as aperoxide, or the catalyst may be oxidised ‘in situ’ by reaction with theoxidant, such as a peroxide reactant.

The olefinic compound for use in the process of the present inventionmay be any organic olefinic compound having at least one olefinic doublebond having the general formula (II).

Wherein R¹, R² and R³ can be the same or different, substituted ornon-substituted and are each independently selected from hydrogen,alkyl, akenyl, aryl, alkaryl, cycloalkyl or alkylcycloalkyl, hydrocarbylgroups. Preferably, R¹, R² and R³ each have less than 30 carbon atoms.More preferably R¹, R² and R³ each have no more than 14 carbon atoms.

In addition any of R¹ R² or R³ can be linked together to form asubstituted or non-substituted ring structure, such as cycloalkyl,cycloalkenyl or alkylcycloalkyl, cyclic hydrocarbyl group, preferablyhaving no more than 14 carbon atoms in total. In a preferred aspect ofthe invention the ring contains from 5 to 12 carbon atoms.

The olefinic compound may be straight-chain, branched-chain or cyclic.Cyclic olefinic compounds include monocyclic, bicyclic or polycyclic.The olefinic compound may be mono-olefinic, di-olefinic orpoly-olefinic. If more than one olefinic bond is present the compoundmay be conjugated or non-conjugated. The olefinic compound may besubstituted by one or more of a halide (e.g. Cl, F, Br, I), an ethergroup, an ester group and/or an allylic hydroxyl. The olefinic compoundmay be a vinyl ester, phenyl or nitrile compound. If substituted by oneor more electron withdrawing groups these should not be substituteddirectly on the olefinic double bond but should be remote therefrom(i.e. at the closest on the carbon alpha to the olefinic bond,preferably more carbons removed from the olefinic bond).

Examples of olefinic compounds which may be used in the presentinvention include but are not limited to hexenes, octenes, decenes,dodecenes, cyclohexenes, styrenes, methylenecyclohexanes and terpenes.Specific examples of olefinic compounds which may be used include butare not limited to dicyclopentadiene, hexadiene, 4-vinylcyclohexene,limonene, cyclooctadiene and cyclohexene.

In the process of the present invention the oxidant is typically in theform of a peroxide. Any suitable peroxide may be used, for examplehydrogen peroxide, an organic hydroperoxide, for example an alkylhydroperoxide or a peroxide ether. Preferably the oxidant is an alkylhydroperoxide, such as tert-butyl hydroperoxide, cumene hydroperoxide,ethylene hydroperoxide or hydrogen peroxide. Most preferably theperoxide is tert-butyl hydroperoxide (TBHP).

The process of the present invention may be performed in neat liquidreagents or a solvent may be used. It is preferred that the process ofthe invention is conducted in the absence of solvent other than thatassociated with the oxidants. For safety reasons the oxidant istypically used in the form of a solution. For example, TBHP is explosiveand is not very stable when neat.

Examples of suitable solvents, which may be used if necessary, includearomatic, alcohol, alkane, ester, ketone or halogenated solvents.Solvents such as 1,2 dichloromethane and toluene are preferred. Watercan be tolerated, typically in an amount of no more than 30% based onthe oxidant.

The process of the present invention is typically performed at aboutatmospheric pressure.

The process of the invention may be performed at any suitabletemperature depending on the reagents, catalysts and solvents used. Theprocess of the invention is typically carried out at a temperature rangeof from 20 and 500° C. The reaction takes place in the reactive sectionof the reactive distillation. Thus, the temperature in the section ofthe column is typically in the range of from 20 and 500° C., for example40 to 200° C. Preferably the reaction temperature in the reactivesection of the column does not exceed the boiling point of the oxidantused.

The actual temperature required in the reactive section will depend onthe volatility of the reagents used and will be known to the personskilled in the art.

In the process of the invention the molar ratio of the olefinic compoundto the oxidant is typically in the range of 0.5:1 to 100:1, preferably1:1 to 20:1, more preferably the molar ratio of olefinic compound tooxidant is about 3.5:1.

The amount of catalyst that is used will depend on the scale of thereaction.

In accordance with the present invention the epoxidation process iscarried out using reactive distillation. Reactive distillation (RD) is aunit operation which combines simultaneous chemical reaction andmulti-component distillation in the same vessel in a single step.

The reactive distillation column used in the present invention comprisesfour essential parts: (i) a reactive section, (ii) a rectifying section,(iii) a stripping section and (iv) a vessel, alternatively referred toas a reboiler.

The reactive section is the section of the reactive distillation columnin which the epoxidation reaction takes place. The catalyst is placed inthis section of the column.

Preferably, the catalyst is held in the reactive section by means of apermeable particle container, also known as a “catalyst packing”. Anysuitable catalyst packing can be used to retain the catalyst in thereactive section of the column. For example, catalyst packing such asknown “envelope shaped” packing may be used. An example of this type ofpacking is KATMAX™ sold by Koch-Glitsh. The present inventors havedeveloped a new “rolled belt shaped” catalyst packing which is suitablefor use in the process of the present invention.

The rolled belt shaped catalyst packing can be used to retain anycatalyst and its potential uses are not restricted to use in the processof the present invention. This catalyst packing is particularly suitablefor use with reusable catalysts.

Another aspect of the present invention is to provide a “rolled beltshaped” catalyst packing (permeable particle container) suitable forcontaining a catalyst such as a catalyst described above. By suitablecatalyst it is meant that the average catalyst particle size is equal toor greater than 0.03 mm. For example from about 0.03 mm to about 2 mm,e.g. from about 0.03 mm to 0.06 mm or 0.14 mm.

The “rolled belt shaped” catalyst packing comprises a belt of mesh. Themess size, i.e. the size of the holes or spaces in the mesh is selecteddepending on factors such as the form and size of the catalyst. The meshsize is typically less than 0.1 mm, although it is envisaged that forsome applications larger mesh sizes could be used. For use in the theepoxidation process of the present invention, the mesh size is typicallyfrom about 0.01 mm to about 0.05 mm, for example 0.02 mm, 0.03 mm or0.04 mm. Typically, the size of the mesh is smaller than the particlesize of the catalyst.

The belt typically comprises two sheets of mesh. These sheets aretypically approximately the same size. The two sheets of mesh areinitially joined together by soldering along three edges. The catalystis then placed between the two layers of mesh and the remaining edge isthen soldered to seal the layers of mesh together. It will beappreciated that the same effect could be obtained by folding a singlemesh sheet and soldering two edges before adding the catalyst and thenonce the catalyst has been added, sealing the remaining edge.

Soldered stripes can optionally be placed on the belt to allow goodcontact of liquid with the catalyst. Once the belt is packed with thecatalyst, the soldered stripes give some curvature to the mesh belt byproviding chambers in the belt which when filled with catalyst createprotrusions, which increases the contact time of the liquid with thecatalyst in the reactive section of the column.

Preferably the stripes are soldered on the belt between 1 and 3 cmapart. The stripes may be placed in any suitable configuration on thebelt. In one preferred configuration the stripes are placed so theirlonger side is parallel to the shorter sides of the belt. The length ofeach stripe is typically less than the length of the short sides of thebelt. For example, the stripes may have a length that is from about aquarter to a third the length of the shorter side of the belt. Typicaldimensions for the stripes are about 0.005 m wide and about 0.020 to0.025 m in length. The size of the stripes does not typically depend onthe size of the belt. The soldered stripes are soldered onto the beltusing solder alloy. Preferably the solder alloy consists of Pb 93.5% Sn5% Ag 1.5% with a melting range between 296 and 301° C. However, itwould be envisaged that if the process is to be carried out at a highertemperature than the above-mentioned alloy melting range then anappropriate high melting point solder alloy or braze alloy could be usedinstead.

The rolled belt can be made of any material which is resistant toorganic chemicals and elevated temperatures. Suitable materials arethose that have sufficient resilience so that the catalyst is held inplace between two pieces of mesh and also have sufficient flexibility toallow the belt to be rolled to the diameter required for it to fitwithin the reaction vessel in which it is used. Examples of suitablematerials which can be used include Teflon and stainless steel. In apreferred aspect of the present invention the rolled belt is made ofstainless steel. The rolled belt shaped packing material is typicallyused to hold the catalyst only. It is preferable that the belt is thin.

Typically, the rolled belt catalyst container of the invention does notrequire a longitudinal support to hold it in place in the reactionvessel in which it is used, such as the reactive section of a reactivedistillation column.

As an example of the use of the permeable particle container describedabove, it may be used in the epoxidation reaction of the invention. Foruse in this process the permeable particle container is packed or filledwith the catalyst and sealed closed so that the catalyst is held in thepermeable particle container. The permeable particle container or beltcontaining the catalyst is then rolled to a suitable diameter so that itfits in the reactive section of the reactive distillation column.

The permeable particle container of the present invention isparticularly suitable for use in liquid phase reactions. The inventorshave surprisingly found that that the permeable particle container helpsto provide optimum residence time in the reactive section of for examplea reactive distillation column and this achieve high conversion of thereactants to the desired product. It has also be found that thisarrangement can provide maximum concentration of the reactants in thereactive section of the reactive distillation column and minimumconcentration of the product in the reaction section of the reactivedistillation column and that this can help reduce by-product formation.The permeable particle container can also provide optimum liquid hold upin the column for the liquid phase reaction. Without wishing to be boundby theory, it is believed that these advantages are due to the structureof the permeable particle container, for example the rolled beltarrangement and the way in which the catalyst material is packed.

In one aspect of the process of the catalyst is held within a permeableparticle container. For example, in a permeable particle container asdescribed above, particularly the rolled belt permeable particlecontainer described above.

The rectifying section is situated above the reactive section and allowsfor the separation of reactants and/or by-products from the desiredproducts. Typically the products have a higher boiling point than thereactants (reagents) and/or the by-products. Thus, the reagents,by-products and products can be referred to as low boiling reactants andhigher boiling products. In this context, the terms “low” and “higher”do not place any particular numerical limit on the boiling points towhich they refer. These terms are simply used to indicate that theboiling point of one material is higher than that of another.

The rectifying section can be connected to a condenser. In a preferredaspect of the invention the rectifying section is situated below acondenser to condense and therefore re-circulate the reagents,preventing the loss of the reagents as vapour.

The stripping section allows for higher boiling point products to beseparated from lower boiling point reagents and/or by-products. Thestripping section is typically heated from the vessel (reboiler).Preferably the stripping section is maintained at a temperature suchthat any reagents present in the stripping section are at least in partint eh vapour phase. The temperature of the stripping section will bemaintained at a level which is higher than that in the rectifyingsection. Preferably, the stripping section is insulated.

The stripping section is located under the reactive section.

The reactive distillation column further comprises one or more inletports for introduction of the reagents into the apparatus and/or one ormore outlet ports for removing products from the apparatus.

The vessel (iv) or reboiler provides a source of heat for the column andis the vessel in which initial vaporisation of one or more of thereagents takes place. The reboiler can also receive the higher boilingpoint product which has been separated in the stripping section.

Typically the reboiler (vessel (iv)) has two ports, one adapted forloading the liquid components into the reboiler and another port at thebottom of the reboiler which is adapted for withdrawing the productsduring the process. The port for loading liquid components into thereboiler may be above the port for withdrawing products. For example,the port for loading liquid components may be at the top, or at least inthe upper half of the reboiler and the port for withdrawing products maybe at the bottom, or at least in the lower half of the reboiler.

Typically the reboiler is supplied with heat. Any suitable heat sourcecan be used. For example, a steam generator may be used. Alternatively,an oil bath or an electrical heat source can be used. The temperature ofthe reboiler will be determined by the energy required to vaporise thereagents and distribute the vapour along the length of the column. Thetemperature will therefore depend on the reagents used and the size ofthe column. The temperature of the reboiler is typically higher than thetemperature of other sections of the column. This is because thereboiler is constantly supplied with heat (e.g. via a steam generator orby an oil bath), whilst the other sections are heated by the vapour ofthe boiling mixture.

In the process of the invention it is preferred that heat is supplied tothe reboiler in the form of steam. The temperature of the reboiler canbe the same or different to that of the reactive section. For example inthe epoxidation of limonene, the reactive section may be at atemperature of from 50 to 100° C. and the reboiler at a temperature of175° C.

In the reactive section, the reaction takes place in the liquid phase.The epoxidation reaction takes place in the liquid phase when thereagents pass over or through the heterogeneous catalyst.

The sections of the reactive distillation column can be connected to oneanother using any suitable means. For example, the reactive section maybe connected to other sections of the column via one or more metalplates. In a preferred aspect of the invention the plates are made ofstainless steel. If necessary, to avoid any leakage appropriate gasketsmay be placed between the plate and the column. It is preferred that thegaskets used in the present invention are Teflon, although other gasketsmay be used providing they are stable to the process of the reaction andthe reaction temperature. Each plate may have one or more inlet portsattached to it. The ports can be used for the introduction of reagentsinto the column. In an aspect of the present invention, one plate ispresent between the reboiler and the stripping section, one between thestripping section and the reactive section, one between the reactivesection and the rectifying section and one between the rectifyingsection and the condenser. This arrangement allows for four potentialpoints for the introduction of the reagents i.e. bottom of the stripingsection (SS), bottom of the reactive section (RS), top of reactivesection (RS) and bottom of the rectifying section (RFS).

The reagents, the olefinic compound and the oxidant can be introducedinto the reactive distillation column at any suitable location. Thereagents can be pre-mixed before introduction into the reactivedistillation column or may be introduced separately. Combinations of thepre-mixing and separate introduction of the reagents can be used.

As explained above, the apparatus used in the invention comprises atleast one inlet port for introduction of the reagents into theapparatus. The apparatus may comprise two or more inlet ports.

The position of the inlet ports which will be used for the introductionof the oxidant and olefinic compound into the column can be varieddepending on the reagents being used and factors such as their relativevolatilities. Possible positions for the inlet ports include, but arenot limited to, a position above the reactive section or below thereactive section. If there is more than one inlet port these can bepositioned together or apart. It will be appreciated that the optimumlocations will depend on the nature of the reagents. As an example theinlet port for the oxidant may be positioned at the top of therectifying section and the inlet port for the olefinic compound may bepositioned at the bottom of the stripping section.

Typically the inlet ports of the lower boiling point reagent would bebelow the inlet point of the higher boiling point reagent.

Typically the reagents are fed to the inlet ports through tubing. Anysuitable tubing which is not reactive with the reagents can be used. Forexample polytetrafluoroethylene (PTFE) tubing can be used.

Typically, a means for controlling the rate of introduction of thereagents is provided. For example, the rate of flow may be controlled bya pump. Any suitable pump such as a peristaltic pump may be used. In apreferred aspect of the invention the flow rate is from 0.5 ml/min to 5ml/min, preferably the operating flow rate of the reaction is about 1ml/min. It will be appreciated that this will depend on the size of thecolumn, the volume of the reactive section and the amount of catalyst.

The diameter of each section of the column will vary depending on thescale of the reaction. For example the diameter of each section of thecolumn may be, but not limited to, from about 0.020 m to about 0.050 m.For example, for larger reactions the column diameter may be in therange of from about 0.2 to about 0.6 m.

The whole column or individual sections may or may not be insulated. Ina preferred aspect the whole column is insulted. Any insulation know tothose skilled in the art may be used, for example Superwool 607™ MAXblanket.

In one aspect, the present invention provides a process wherein:

(i) a proportion of the reagents is placed in the vessel (iv) and heatedto a temperature where vaporisation occurs, and

(ii) the reagents from the vessel (iv), in the form of vapour, risethrough the column heating the sections of the column, and

(iii) when the column reaches a steady state temperature, inlet portsare opened to allow the continuous flow of the reagents into the columnat the same rate as the product is removed from the vessel (iv).

In the figures:

FIG. 1 shows an example of a reactive distillation column of the typeused in the present invention.

FIG. 2 shows the rolled belt shaped catalyst packing

FIG. 3 shows the percentage conversion of TBHP in the process of thepresent invention using the reactive distillation column dependant onthe ratios of cyclohexene to oxidant.

FIG. 4 shows the percentage conversion of TBHP for cyclohexeneepoxidation in the process of the present invention using the reactivedistillation column relative to the feed positions on the column.

FIG. 5 shows the TBHP conversions in the process of the presentinvention using the reactive distillation column relative to the flowrate of the reagents into the column.

FIG. 6 shows the percentage yield of 1,2-limonene epoxide in the processof the present invention using the reactive distillation columndependant on the ratios of limonene to oxidant.

FIG. 7 shows the percentage yield of 1,2-limonene epoxide in the processof the present invention using the reactive distillation column relativeto the feed positions on the column.

The reactive distillation column as shown in FIG. 1 comprises acondenser (1), a rectifying section (2), a catalytic reactive section(3), a stripping section (4), a reboiler (5), a steam generator (6),thermocouples (T) and inlet ports (7) and (8) for introducing into thereactive distillation column the oxidant and olefin independently andvia peristaltic pumps (9) and (10), which are calibrated to control theflow rate of the reactants.

It is preferred that both reagents are at least initially introducedinto the reboiler at room temperature. The reagents are then heated inthe reboiler. When the liquids start to vaporise and the vapours move upthe column, the temperature of the column increases until the reactivedistillation column reaches total reflux. When the temperature of thereactive distillation column reaches steady state, the reactants can beintroduced to the column at specified locations via inlet ports (7) and(8).

The temperature in the reactive section will depend on the boiling pointof the reagents used and is held at such a temperature to maintain theolefin in the vapour phase and the oxidant at least partially in thevapour phase.

The reflux temperature will vary depending on the reagents used. Forexample the temperature in the reactive section may be held at about 80°C. for certain combinations of reagents. It is important that thetemperature of the reactive section is monitored as this is thetemperature at which the reaction takes place. The temperature in theother sections of the column can also be monitored. This will giveinformation on the functioning of the system as a whole. It is alsoimportant as the temperatures in these sections will indicate when asteady state has been reached.

The resultant product epoxide will have a higher boiling point than thestarting reagents and typically the boiling point of the product will behigher than that of any by-products. The product epoxide can then beremoved from the bottom of the reboiler in the form of a liquid as ithas a higher boiling point than either the starting olefinic compound orthe oxidant.

The present invention will be explained in more detail with specificreference to the epoxidation of cyclohexene with TBHP.

The PBI.Mo catalyst is prepared as described in U.S. Pat. No. 5,420,313and then added to the ‘rolled belt shaped’ catalyst packing. The packingis then placed into the reactive section of the reactive distillationcolumn. The initial reaction mixture in the reboiler is then heated toabout 100° C. which causes the reagents to reflux, resulting in bothreagents entering the vapour phase and passing through the reactivesection containing the catalyst. After about 30 minutes the temperatureof the column reaches steady state and the temperature reaches about 74°C. at the bottom and about 71° C. at the top of the reactive section(this temperature might vary depending of the TBHP:cyclohexene ratio).TBHP is then fed into the rectifying section of the column above thereactive section. Cyclohexene is simultaneously fed into the strippingsection of the column below the reactive section. The molar ratio of theTBHP and cyclohexene feeds is preferably about 1:3. The productepoxycyclohexane can be continuously withdrawn from the bottom of thereboiler as a liquid.

Another example is the epoxidation of limonene with TBHP.

The reactive distillation column is set up as previously described. Theinitial reboiler mixture of TBHP and limone is then heated to about 180°C. which causes the reagents to reflux, resulting in both reagentsentering the vapour phase and passing through the reactive sectioncontaining the catalyst. After about 30 minutes the temperature in thecolumn reaches steady state and the temperature reaches about 80° C. atthe bottom of the reactive section and about 77° C. at the top of thereactive section (these temperatures might slightly vary depending onthe TBHP:limonene ratio). TBHP is then fed into the stripping section ofthe column below the reactive section of the column. Limonene issimultaneously fed at the top of the reactive section. The molar ratioof the TBHP and limonene feeds is preferably about 1:3. The productlimonene 1,2-epoxide can be continuously withdrawn from the bottom ofthe reboiler as a liquid.

The present inventors have surprisingly found some significant andunexpected advantages associated with conducting epoxidation reactionsin the manner used in the present invention. These advantages caninclude one of more of the following:

Higher levels of conversion can be achieved in comparison to batchreactions, side reactions and by-product production can be reduced,improvements in selectivity can be achieved, the amount of catalystrequired to produce the same degree of conversion can be reduced whencompared to batch processes, and processing advantages such as easiertemperature control and eliminating the use of large quantities offlammable solvents can be obtained.

These and other advantages can lead to reduced production costs.

The invention is illustrated by the following non-limiting Examples.

Preparation of Catalyst Composition (PBI.Mo Catalyst)

A catalyst composition comprising molybdenum complexed to apolybenzimidazole porous resin (PBI.Mo) was prepared using the followingprocedure (see Scheme 1):

10 g of wet polybenzimidazole porous resin beads, AUROREZ (trade mark,Hoechst-Celanese) was stirred with 1 M sodium hydroxide solutionovernight, washed with deionised water until pH=7, washed with acetoneand then dried under vacuum at 40° C. The nitrogen content of the resinwas then determined by microanalysis to be 15.10% which, given thatthere are two nitrogen atoms in each imidazole repeat unit in thepolymer, gives a ligand (imidazole) loading on the polymer of 5.39 mmolg⁻¹.

Typically for the synthesis of the PBI.Mo catalyst 5 g of the aboveresin (0.027 mol imidazole group) was refluxed with molybdenumacetylacetonate MoO₂(acac)₂ (17.68 g, 0.054 mol Mo) in anhydrous toluenefor a period of four days. The resin beads changed colour from brown togreen. The resulting catalyst composition was collected by filtrationand then extracted with acetone in a Soxhlet apparatus for 48 hours.During extraction a dark blue colour was evident in the extractingsolution, which disappeared eventually upon repeated introduction offresh colourless solvent. The catalyst beads were then dried in a vacuumoven at 40° C.

Following grinding of a small sample of the PBI.Mo catalyst anddissolution in aqua regia, the resultant solution was made up with waterbefore analysis by atomic absorption spectroscopy. From five replicateseparate PBI.Mo catalyst preparations this yielded an average value forthe Mo content of the catalyst of 0.95 mmol Mo g⁻¹. The correspondingaverage ligand (imidazole) loading from elemental microanalysis was 2.03mmol g⁻¹, giving an average ligand: Mo mole ratio of 2.4:1.

The catalyst composition was activated prior to use in epoxiationreactions by refluxing with tert-butyl hydroperoxide in1,2-dichloroethane using a mole ratio of Mo:tBHP of 1:80 during whichthe catalyst beads turned a yellow colour. When not in use the activatedcatalyst compositions were stored in a closed jar.

Particle size distribution measurement of the catalysts was carried outusing Malvern Mastersizer. BET surface area measurements were carriedout by the nitrogen adsorption and desorption method using aMicromeritics ASAP 2010 (Accelerated Surface Area and Porosimetry). Themetal loading data, corresponding ligand/metal ratio and physicalproperties of polymer-supported Mo (VI) catalysts are presented in Table1.

TABLE 1 Mo loading and Mo/ligand ratio and physical properties ofpolymer- supported Mo catalyst Properties PBI.Mo catalyst Mo loading(mmol Mo/g resin)^(a) 0.95 Ligand loading mmol/g resin^(b) 2.3 Ligand/Moratio 2.4:1 Particle size 10% below 228 μm; 90% below 331 μm BET surfacearea 22.12 (±0.3) m²/g ^(a)From AAS analysis of digested resins.^(b)From N % elemental analysis of Mo loaded resins assuming ligand =imidazole or aminomethyl pyridine as appropriate.

Preparation of tert-butyl Hydroperoxide (TBHP)

t-Butyl hydroperoxide (70%) from the Aldrich Chemical Co. was renderedanhydrous by Dean-Stark distillation from a toluene solution followingthe modified method that was previously reported by Sharpless andVerhoeven [Sharpless, K. B.; Verhoeven, Aldrichim. Acta 12 (1979) 63.].The molarity of TBHP was determined by iodimetry. The concentration ofthe TBHP in toluene was found to be 3.65 mol/dm³.

GC Analysis

All the reactant and product compositions were analysed by gaschromatography. HP 5080 II Gas Chromatograph (GC) was used to analysethe composition of samples from the liquid phase of the reactivemixture.

The GC was fitted with a 30 m long J&W DB-5 MS, 0.32 mm diameter and0.25 μm film capillary column with an FID detector. Both injector anddetector temperatures were set at 473 K and helium carrier gas flowmaintained at 1 ml/min (split ratio 100). For cyclohexene epoxidationcolumn temperature was programmed between 313 and 473 K (313 K for 4.5min, then ramp 25 K/min until 473 K). The sample size for GC was 0.4 μLand a complete GC run took about 11 min.

For the epoxidation of limonene column temperature was programmedbetween 323 and 473 K (323 K for 5 min, then ramped 4 K/min until 388 Kand finally ramped 30 K/min until 473 K). The sample size for GC was 0.3μL and a complete GC run took about 25 min (split ratio 100).

Preparation of the Catalyst Packing

Two mesh sheets, typically of the same size, were cut out of larger meshsheet(s). The two sheets of mesh were initially joined together bysoldering along three edges.

Then solder stripes were added by soldering through two layers of themesh, joining two sides of the belt. The stripes were placed in apattern within a distance of 0.03 m from each other in one line as shownin FIG. 2. The catalyst (50 g) was then placed between the two layers ofmesh and the remaining edge was then soldered to seal the layers of meshtogether. The same effect could be obtained by folding a single meshsheet and soldering two edges before adding 50 g of the catalyst andthen sealing the remaining edge. The catalyst containing belt was rolledup and placed into the reactive section of the column.

Typical Epoxidation Procedure

Cyclohexene and TBHP solution in toluene were weighted and introducedinto the reboiler at an appropriate molar ratio. The reaction mixturewas heated by steam circulated through the coil of the reboiler or by anoil bath. Once the temperature recorded by thermocouples placed alongthe column achieved the steady state, the column was heated for 1 hour.The temperature of the liquid recorded at the bottom and top of reactivesection was 71° C. and the temperature of the vapour was 74° C. Thereactants were fed in through the inlet ports, with the oxidant inletport positioned above the reactive section and the olefin inlet portpositioned below the reactive section, maintaining the same mole ratioof cyclohexene to TBHP as was used in the reboiler. Once the reactantswere being pumped into the column, product withdrawal from the bottom ofthe reboiler was started, maintaining the same flow rate as that used tointroduce the reactants into the column. After one hour of feeding thereactants into the column, samples were taken from the reboiler andother locations of the column for analysis. The process was continuedfor another hour and samples were withdrawn periodically for analysisand finally the process was stopped. Once the column was cooled, theliquid from the reboiler was drained and analysed.

All the chemicals used for this study were purchased from AldrichChemical Company Inc. and they were used without further purification.

Epoxidation of Cyclohexene in Reactive Distillation Column

For the lowest studied cyclohexene:TBHP mole ratio of 1.5:1, 80% TBHPconversion was achieved. Further increase of cyclohexene:TBHP ratios to2:1, 2.5:1, 3:1 and 3.5:1 increased the TBHP conversion to 86% 90% 91%and 95%, respectively. The optimum conversion of TBHP (95%) was obtainedfor 3.5:1 cyclohexene:TBHP mole ratio. Increase of reaction rate andTBHP conversion with an increase in cyclohexene:TBHP mole ratio wasalready found in batch studies carried out in our earlier work. However,for continuous epoxidation in the RDC the increase of cyclohexene:TBHPmole ratio above that optimal ratio (3.5:1) resulted in slight reductionof TBHP conversion. It can be seen that for cyclohexene:TBHP mole ratioof 5.5:1, TBHP conversion dropped to 92%. At very high mole ratio ofcyclohexene:TBHP, because of relatively low boiling point (82° C.) andhigh volatility of cyclohexene the reflux in the column was veryvigorous and most of the unreacted cyclohexene reached the top of theRDC. Because of vigorous reflux in the column the residence time of thereactants in the reactive section of the column was reducedsubstantially, which resulted in lower TBHP conversion for very highcontents of cyclohexene in the RDC. It is to be noted that forcyclohexene:TBHP mole ratio of above 5.5:1 the column had significantflooding.

The column was designed in a way to allow feed substrates at fourdifferent locations i.e. bottom of the stripping section (SS), bottom ofthe reactive section (RS), top of the reactive section (RS), and top ofthe rectifying section (RFS). The boiling point of the solution of TBHPin toluene is higher than cyclohexene and therefore TBHP was fed abovethe cyclohexene feed point in the RDC. Apart from standard feed position(TBHP at the top of the RS, cyclohexene at the bottom of the RS) used inthe feed mole ratio runs we studied three other possible positions. Forall feed position experiments cyclohexene:TBHP ratio of 3.5:1 wasemployed. As shown in FIG. 4 the THBP conversion for standard experimentwas already high (95%) the differences in conversion for other feedposition have not been significant. However, the highest TBHP conversion(98%) was obtained when TBHP was fed at the top of the rectifyingsection and cyclohexene was introduced at the bottom of the stripingsection. These feed positions are the two most distant possible feedingpoints.

In feed mole ratio and feed position studies we used TBHP flow rate of 1ml/min. For this flow rate 98% TBHP conversion was obtained.

It is shown in FIG. 5 that the increase of TBHP flow rate reduced TBHPconversion. To keep the same reactants mole ratio both TBHP andcyclohexene flow rate were increased. However, the flow rate of TBHP isimportant because it is the limiting reactant for this system.Increasing the TBHP flow rate to 2.2 and then 3.4 ml/min slightlyreduced the TBHP conversion to 94% and 93%, respectively. Furtherincrease of TBHP flow rate to 4.2 ml/min decreased the TBHP conversionalmost by 10% compared to the lowest TBHP flow rate of 1 ml/min.

Epoxidation of Limonene in Reactive Distillation Column

Similar optimisation studies as those performed on cyclohexne wereperformed using limonene as the olefin. It can be seen from FIG. 6, thatthe best conversions to the epoxide were achieved when using a ratio ofolefin to oxidant of 4:1.

It can also be seen in FIG. 7 that the optimum positions for the inletports when limonene is used as the olefin is when the TBHP is introducedat the bottom of the reactive section and limonene is introduced at thetop of the rectifying section.

1.-30. (canceled)
 31. A permeable particle container comprising twosheets of mesh, or one sheet of mesh folded, sealed by solder along theedges, leaving one edge open to allow for the addition of particulatematerial, which edge is solderable to seal the particle container,wherein the mesh has flexibility that allows the container to be rolled;wherein the particle container comprises soldered stripes that are from1 to 3 cm apart.
 32. A container according to claim 31, wherein thestripes are positioned so that their longer side is parallel to theshorter side of the container.
 33. A container according to claim 31,wherein the length of each stripe is less than the length of the shortside of the container.
 34. A container according to claim 31, whereinthe stripes are about 0.005 m wide and about 0.020 to 0.025 m in length.35. A container according to claim 31, wherein the mesh size is lessthan 0.1 mm.
 36. A container according to claim 35, wherein the meshsize is from about 0.01 mm to about 0.05 mm.
 37. A container accordingto claim 31, wherein the particulate material is a catalyst.
 38. Acontainer according to claim 37 wherein the catalyst is an epoxidationcatalyst.
 39. The use of a container according to claim 38 in acontinuous expoxidation process.